Conventional shaft seals are unable to seal fluids in applications with excessive shaft-to-bore misalignment or dynamic shaft runout, due to the inability of the circular lip to follow the shaft surface. When the shaft axis is displaced radially relative to the axis of the bore, the sealing lip is compressed in the direction of shaft displacement, while the sealing lip on the opposite side often loses contact with the shaft.
Various attempts have been made in the prior art to solve this problem, such as by providing a shaft seal with a more flexible flex section, by varying garter spring load and/or lip interference, and by molding an annular rubber bead below the lip. These attempts to solve the problem have helped, however, they have not prevented the tendency for the lip to take an oval shape and leak.